The present invention relates to an apparatus and method of forming a metal oxide film such as a tantalum oxide film suitable for an insulating film. The present invention also relates to an apparatus and method of modifying a metal oxide film.
Generally, to manufacture a semiconductor device, a semiconductor wafer is repeatedly subjected to a film formation process and a pattern etching process, thereby manufacturing a desired device. Particularly, specifications of a film forming technique are becoming stricter year by year as the density and integration of semiconductor devices become higher. For example, a very thin oxide film such as the insulating film of a capacitor or gate insulating film in a device is required to be thinner, and simultaneously, good insulating properties are required.
As the insulating film, a silicon oxide film or a silicon nitride film can be used. However, a metal oxide film such as a tantalum oxide (Ta.sub.2 O.sub.5) film tends to be used recently as a material having better insulating characteristics. The metal oxide film exhibits highly reliable insulating properties although the film is thin. When the surface of the metal oxide film is modified after the film formation process, the insulating properties can be further improved. This technique is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-283022 (to be referred to as related art 1 hereinafter.
Formation of a metal oxide film, e.g., a tantalum oxide film will be described below. The metallic alkoxide of tantalum (Ta(OC.sub.2 H.sub.5).sub.5) is used as a film formation material, as disclosed in prior art 1. The metallic alkoxide of tantalum is bubbled with nitrogen gas or the like and supplied while keeping a semiconductor wafer at a process temperature of about 400.degree. C. With this process, a tantalum oxide film (Ta.sub.2 O.sub.5) is formed by CVD under a vacuum atmosphere.
To further improve the insulating properties as needed, the semiconductor wafer is loaded into an atmosphere containing ozone. A UV ray from a mercury lamp is irradiated to ozone under the atmospheric pressure to generate active oxygen atoms. The tantalum oxide film is modified using the active oxygen atoms, thereby obtaining an insulating film having more satisfactory characteristics.
In formation of an insulating film in a semiconductor device, it is important to improve the properties of the insulating film, as described above. Simultaneously, high productivity, i.e., a high throughput is required to mass-produce high-quality devices. The above-described film formation and modification processes take a long time, and the throughput is not so high.
In the film process, the growth rate of the tantalum oxide film is about 1 to 2 nm/min, and a great challenge is to largely increase the growth rate of the metal oxide film. In the modification process, about 30-minute modification process must be normally performed for one wafer to obtain a practical breakdown voltage, although the process time changes depending on the amount of UV rays or ozone. Accordingly, the throughput is insufficient to result in a high cost.
A technique of increasing the growth rate is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-247650 (to be referred to as related art 2 hereinafter) in which an azeotropic organic solvent containing alcohols such as ethanol is added to the metallic alkoxide as a material for film formation, and the resultant mixture is vaporized and supplied into the film forming apparatus, thereby performing the film formation process.